Diaphragm or membrane valves are known in the art. The flexible diaphragm is secured between two mating faces of the valve body, sometimes serving as a gasket or seal there between, and forms two discrete chambers by completely covering two more or less symmetrical shallow indentations fabricated in the joined faces. One of the chambers is connected by suitable ports or vents to a source of gas or liquid under pressure sufficient to force the diaphragm to stretch and flatten against the surface of the mating indentation that comprises the second chamber. This second chamber is ported to the exterior of the valve body by an inlet and outlet channel through which the product liquid or gas flows through respective piping or tubing connected to the valve body. Product fluid flows freely through the valve chamber until pressure is applied in the control chamber to cause the diaphragm to press against the inlet-outlet ports and stop the flow.
Mechanical valves of prior art may have more than two ports and the flow of fluid between the plurality of channels is controlled and directed by movable plugs or plates having apertures therethrough that align with selected channels when suitably positioned. Such valves are subject to the usual problems of mechanical valves, e.g. wear on moving parts, packing leaks, inaccurate positioning in open and close position, corrosion and the like.
Two-channel diaphragm valves, as above described, are often combined in groupings or arrays to obtain a variety of liquid flow patterns in blending, metering, filling and other operations. While such groupings are useful and necessary, they are usually complex, hence difficult to assemble, connect and control because of the number of valves required. Even when many valves are contained in a single housing, as taught by J. G. Smith et al, USP Pat. No. 3,176,714, the device is difficult to manufacture and to maintain in service, as can be envisaged by the task of repairing a single failed membrane in the system.
Dosing cylinders with double acting pistons are known in the art, in which product fluid under pressure is admitted to one end of the cylinder in which the piston is mounted. This forces the piston to the other end of the cylinder, displacing product fluid therefrom via an exit port. Each time the cycle is reversed, an accurately metered amount of fluid is expelled from alternate sides of the piston. Such a system requires a minimum of four valves for operation, and corresponding pressure controls if said valves are of the diaphragm type.
Means for axially adjusting the position of one end wall of the cylinder of such devices, whereby to change the cylinder volume, and thus the metered amount of fluid, are also known in the art.